Cancer diagnosis as a discipline has been greatly improved with the advent of tumor imaging technologies which use radiolabeled monoclonal antibodies or their fragments to target primary and metastatic lesions in not detected by standard MRI or CAT scans. Serum markers, which generally use monoclonal antibodies to tumor cell products, have also helped the clinician to quantitate the size of the tumor burden and this information has helped to determine the effectiveness of treatment at the completion of each course of therapy. What is lacking is a method which can monitor the efficacy of cytoreductive therapy (chemotherapy, radiotherapy, or immunotherapy) during initial treatment to help the clinician know whether his/her chosen therapy is effective before a commitment to a given approach has been made. The ability to make this determination may enable clinicians to spare the patient undue toxicity if a given treatment approach appears unsuccessful and buy valuable time by enabling the therapist to switch to alternative treatment before actually completing each round of therapy. Imaging is an ideal tool for making this determination since it is non-invasive, rapid, and relatively inexpensive to perform. Our laboratory has developed a monoclonal antibody which targets necrotic regions in tumors and is especially effective in binding newly degenerating cells regardless of their cell of origin or disease status. In this proposal, we intend to construct a fast- clear derivative which after radiolabeling can be used to quantitative the amount of necrosis before and after therapy. Genetic engineering methods will be used to construct a single chain, diabody, and triabody derivative as well as F(ab) and F(ab')2 fragments of chimeric monoclonal antibody TNT-3. In vitro binding studies and in vivo biodistribution and imaging analyses will be used to determine which of the above constructs have the best imaging characteristics. At the completion of this phase of the work, in vivo tumor models consisting of chemotherapy resistant and sensitive tumor sublines will be used to demonstrate the potential of this approach to monitor the effectiveness of cytoreductive therapy. The results of these studies could provide the basis for future clinical trials by providing the nuclear medicine physician, oncologist, and radiation therapist with a new and valuable tool to assess the effectiveness of standard and experimental cancer therapy in a cost-effective and timely manner.